Aerial field simulation

ABSTRACT

Any arbitrary antenna array distribution can be represented as the sum of a symmetric and an antisymmetric function. The radiation at any point in the far field of the aerial array can then be simulated by adding together the symmetric and antisymmetric outputs in quadrature with the correct amplitude. This simplifies the construction of subsequent combining units since these reproduce the far field at any point by amplitude wieghting along without the need for differential phasing.

United States Collins 1 1 54 AERIAL FIELD SIMULATION 3,255,450 6/1966Butler ..343/854 3,056,961 10/1962 Mitchell [75] Invent "F Comm welwy3,175,156 3/1965 Sletten ..343/854 Garden C1ty, England [73] Assignee:International Standard Electric Cor- Primary Examiner-E Liebermanporation, New York y Attorney-C. Cornell Remsen, Jr. et al.

[22] Filed: July 21, 1971 57 ABSTRACT PP 1641758 Any arbitrary antennaarray distribution can be represented as the sum of a symmetric and anan- 52 us. 01 ..343/100 AP, 343/703 Symmetric functiOn- The at any 51Int. Cl G015 7/40 field aerial be Simulated by 581 Field of Search..343/844 853 8541 adding meme symmetric antisymmemc 343/100 R 6 puts inquadrature with the correct amplitude. This simplifies the constructionof subsequent combining units since these reproduce the far field at anypoint [56] References Cned by amplitude wieghting along without the needfor dif- UNlTED STATES PATENTS ferential phasing.

3,267,472 8/1966 Fink ..343/854 4Claims, 1 Drawing Figure I 4x13: 0qymmet/y l-Q7 1 ..1 l 5 rd I ||P- 7: 7: 7 4

1 (am/71in Unit 9 l l// l PATENTEU W 81915 Inventor ROB/N A, COLL/N5 WWAgent AERIAL FIELD SIMULATION BACKGROUND OF THE INVENTION This inventionrelates to aerial arrays and to a method of simulating the far field ofa symmetrical aerial array for monitoring purposes.

SUMMARY OF THE INVENTION It is an object of the present invention toprovide a dividual aerials, combining the sampled currents so as toproduce symmetric and antisymmetric functions, and adding the symmetricand antisymmetric functions in quadrature with predetermined amplitudeweighting.

Any arbitrary aerial array distribution can be represented as the sum ofa symmetric and an antisymmetric function. Samples of the currents onthe individual aerials making up the array can then be combined toreproduce these symmetric and antisymmetric functions. The radiation atany point in the far field of radiation of the aerial array can then besimulated by adding together these symmetric and antisymmetric outputsin quadrature with the correct amplitude weighting.

The division of the array distribution into symmetric and antisymmetriccomponents simplifies the construction of the subsequent combiningunits, since these then reproduce the far field at any point byamplitude weighting alone, without the need for differential phasmg.

The invention will now be further described with reference to theaccompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWING The sole drawing illustrates an arrayof four dipole antennas symmetrically placed, together with therequisite combining and weighting units.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, thereis shown a linear array of four dipole antennas 1,2,3 and 4 identifiedby E E E E which also represent the R.F. voltages on the elements in thearray. The time varying factor e""' is ignored for simplicity. Ingeneral the E's are arbitrary complex numbers and may each represent thesum of several R.F. voltages at different frequencies without loss ofgenerality unless the frequencies are sufficiently spread to limit theaccuracy of the system as a result of the limited bandwidth ofsubsequent devices. Each of these dipoles is monitored for current flowin the dipole. As described in applicant's copending application Ser.No. 164,759, filed July 21, l971, the radiated field of a dipole at anypoint is directly related in amplitude and phase to the current in thedipole arms. This can be sampled by a slot cut in the dipole arm. Thevoltage across this slot is fed to a transmission line which may bematched to subsequent processing units by the suitable positioning of aresistor. This enables both the RF current from the power feed to thedipole and the current produced by interaction with other radiatedelements to be measured. The current samples are applied in symmetricalpairs to phase shifting hybrid arrangements 5 and 6 denoted HRl and HR2,and from these to weighting networks 7, 8, 9 and 10 denoted C1, C2, S1,and S2 respectively, and thence to combining unit 11, all of which willbe referred to in due course.

The voltage in the far field at an angle 0 to the center line of thearray may be written as:

=f( 11 f( 0) 1) In this expression, the first factor is a factordependent on radial distance alone of the array, the second factor is afactor dependent on 0 alone, and corresponds to the polar diagram forindividual antenna elements of the array, and the third factor,describes the variations which arise owing to the differing distances dof the complex sources E on either side of the center point of thearray. For the symmetrical array shown, only two distances d, and d areconcerned, positive and negative values being taken for the respectivesides of the array, positive on the left, negative on the right, and )tis the wavelength at the particular radiation frequency being studied;and e andi have their usual significance in complex algebra. The thirdfactor may then be expanded to read dz Sin 0 I e This expression wouldcontinue for as many factors as there are antenna elements, but in thiscase terminates with the fourth.

Equation (2) contains all the variation in V due to variation in the Es.It is this factor it is required to reproduce in order to simulate theeffect in V of changes in the E s.

One method of doing this is to take samples of all the Es and insertcables of different phase lengths d) (1) (1)., where and l is anarbitrary fixed length for all the cables concerned between therespective monitoring points and hybrid networks 5 and 6; The sum ofthese is then proportional to the third factor in (1) above (i.e.equation 2). However, where there are a large number of elements in thearray and it is required to simulate the far field at more than oneangle 0, a worthwhile simplification results if we replace this phasingof the samples by weighting in amplitude alone. This can only be done ifthe array is symmetrical.

Re-writing the expression for the last factor above:

=(E E cos d sin 9) (E l E cos d sin 6) sin d1 sin (E;- E sin d sin Thisin fact corresponds to the division of the arbitrary array distributioninto two components, asymmetric one (E +E E +E and an antisymmetric one(E -E E E This can'saaaabfiisnshzasyn'eaas an set of 180 hybrid rings asindicated at HR! and HRZ in the drawing. Expression (3) can then bereproduced by amplitude weighting of the symmetric and antisymmetricoutputs from these rings with weights:

C =Cos (217M d,Sin0) C Cos (Zn-lit d Sin6) S Sin (211M d Sin0) S Sin(21r/h d Sin0) which are readily derived for any required angular 0since all the constants are known. These outputs are then added in acombining unit 11 to give an output proportional to the far field at 6;the factor i in expression (3) means that an extra quarter wavelength ofline is necessary in the antisymmetric side. This, however, is the samefor all angles 6. As shown in the drawing, combining unit 11 includeshybrid circuit 12, and adders l3 and 14.

This system is readily extended to any symmetric array containing aneven number of elements. It can also be applied if there is an elementon the center line, i.e. an odd number of elements. In this case, thecenter element only contributes to the symmetric component of the arraydistribution and not to the antisymmetric component, so that its hybridring or equivalent unit can be dispensed with, and the sample merelyadded to the symmetric side of the combining unit with appropriateweighting.

It is to be understood that the foregoing description of specificexamples of this invention is made by way of example only and is not tobe considered as a limitation on its scope.

I claim:

1. A method of simulating the far field at any arbitrary point thereofof any arbitrary symmetrical aerial array comprising:

sampling the radio frequency currents flowing instantaneously within theindividual aerials; combining the sampled currents in symmetrical pairsto phase shifting hybrid arrangements so as to produce symmetric andantisymmetric functions with respect to the center line of the array;applying predetermined amplitude weighting to the individual samples;and

adding the symmetric and antisymmetric functions in quadrature to obtaina representative output.

2. A method according to claim 1 wherein said array contains an evennumber of aerial elements spaced symmetrically about a center line ofsaid array.

3. A method according to claim 1 wherein said array contains an oddnumber of aerial elements, of which the central element is placed at thecenter line of the array and the remainder are spaced symmetrically oneither side thereof, said cen ral element being associated with thoseelements from which there are derived said symmetrical functions.

4. An apparatus for simulating the far field at any arbitrary pointthereof of any arbitrary symmetrical aerial array comprising:

means for sampling the current flowing within each aerial of said array;

phase shifting hybrids connected in symmetrical pairs to the samplingmeans for combining said current samples into symmetric andantisymmetric pairs;

a plurality of weighting networks for weighting each output of saidmeans for combining; and

a combining unit for combining said symmetric and antisymmetric pairs inquadrature.

1. A method of simulating the far field at any arbitrary point thereofof any arbitrary symmetrical aerial array comprising: sampling the radiofrequency currents flowing instantaneously within the individualaerials; combining the sampled currents in symmetrical pairs to phaseshifting hybrid arrangements so as to produce symmetric andantisymmetric functions with respect to the center line of the array;applying predetermined amplitude weighting to the individual samples;and adding the symmetric and antisymmetric functions in quadrature toobtain a representative output.
 2. A method according to claim 1 whereinsaid array contains an even number of aerial elements spacedsymmetrically about a center line of said array.
 3. A method accordingto claim 1 wherein said array contains an odd number of aerial elements,of which the central element is placed at the center line of the arrayand the remainder are spaced symmetrically on either side thereof, saidcentral element being associated with those elements from which thereare derived said symmetrical functions.
 4. An apparatus for simulatingthe far field at any arbitrary point thereof of any arbitrarysymmetrical aerial array comprising: means for sampling the currentflowing within each aerial of said array; phase shifting hybridsconnected in symmetrical pairs to the sampling means for combining saidcurrent samples into symmetric and antisymmetric pairs; a plurality ofweighting networks for weighting each output of said means forcombining; and a combining unit for combining said symmetric andantisymmetric pairs in quadrature.